1. Technical Field
The present invention relates a method for manufacturing molten iron and an apparatus for manufacturing molten iron that are capable of stably charging and discharging fine iron ore quickly during an emergency situation.
2. Background Art
The iron and steel industry is a core industry that supplies the basic materials needed in construction and in the manufacture of automobiles, ships, home appliances, and many of the other products we use. It is also an industry with one of the longest histories that has progressed together with humanity. In an iron foundry, which plays a pivotal roll in the iron and steel industry, after molten iron, which is pig iron in a molten state, is produced by using iron ore and coal as raw materials, steel is produced from the molten iron and then supplied to customers.
At present, approximately 60% of the world's iron production is realized by using the blast furnace process developed from the 14th century. In the blast furnace process, coke produced by using bituminous coal and iron ore that have undergone a sintering process are charged into a blast furnace, and hot gas is supplied to the blast furnace to reduce the iron ore to iron, to thereby manufacture molten iron. However, in the blast furnace process, there are problems in that accessory equipment is necessary to manufacture coke and sintered ore, and environmental pollution is very severe due to the accessory equipment.
In order to solve the above problems of the blast furnace process, a smelting reduction process has been developed and researched by many countries. In the smelting reduction process, molten iron is manufactured in a melter-gasifier by directly using raw coal as a fuel and a reducing agent and iron ore as an iron source. Here, oxygen is injected through a plurality of tuyeres installed in an outer wall of the melter-gasifier, a coal-packed bed in the melter-gasifier is burned, and then molten iron is manufactured. The oxygen is converted into a hot reducing gas and is transferred to a fluidized-bed reduction reactor. Then, the hot reducing gas reduces fine iron ore and is discharged outside.
The fluidized-bed reduction reactor reduces fine iron ore with a grain size that is equal to or less than 8 mm. The fine iron is fluidized in a reducing gas flow and then reduced in the fluidized-bed reduction reactor. That is, the fluidized-bed reduction reactor reduces fine iron ore by interacting a reducing gas as a gas with fine iron ore as a solid. The fluidized-bed reduction reactor includes a cyclone and a distribution plate. Nozzles are regularly arranged in the distribution plate. Here, the cyclone includes a cone portion located in an upper portion thereof and a dipleg portion located in a lower portion thereof. A reducing gas is ejected toward the upper portion while entering from the lower portion of the fluidized-bed reduction reactor and passing through the distribution plate. Since a plurality of distribution nozzles are installed on the distribution plate, the reducing gas can be ejected with a high speed toward the upper portion of the distribution plate. The cone portion of the cyclone located in an upper portion of the fluidized-bed reduction reactor collects fine iron ore and re-transfers it to the lower portion of the fluidized-bed reduction reactor through the dipleg portion.
The reducing gas passing through the distribution plate uniformly flows over an entire area of the fluidized-bed reduction reactor. However, when the fine iron ore is charged into the fluidized-bed reduction reactor in an early operating time, the fluidized bed is not formed up to the height of the lower end of the dipleg portion. In the dipleg portion, the reducing gas flows at a high speed toward an upper portion thereof through an inside thereof. Therefore, when the dipleg portion is not sealed, the fine iron and the reducing gas flow back to rise toward the cone portion through the dipleg portion.
The fine iron scattered in the upper portion of the fluidized-bed reduction reactor is collected in the cone portion of the cyclone and re-circulated toward the lower portion of the fluidized-bed reduction reactor. Therefore, backflowing fine iron and scattered fine ore collide with each other and then the dipleg portion is blocked. Furthermore, there is a phenomenon in which the dipleg portion is blocked due to detachment of a coating layer inside the cyclone. As described above, since a large load is applied to another cyclone if the dipleg portion is blocked and the cyclone does not operate well, a large amount of fine iron is discharged outside of the fluidized-bed reduction reactor. In this phenomenon, although backflow of the fine iron toward the dipleg portion is largely reduced if the fluidized bed is formed up to the dipleg portion as the fine iron ore is discharged and then the dipleg portion is sealed by the fluidized bed, there is a problem in that initial operation of the fluidized-bed reduction reactor is unstable.
Meanwhile, if a flow of the fine iron ore between the fluidized-bed reduction reactors is not normal due to an unstable operation of the fluidized-bed reduction reactors, the height of the fluidized bed rises to equal to or above the discharging passage of the fine ore. The pressure of a quencher is controlled to be lower than that of the fluidized bed by using another discharging passage to lower the height of the fluidized bed. The height of the fluidized bed can be lowered by discharging fine ore into the quencher by force by using the pressure difference. However, as a flow of the reducing gas of the fluidized bed is concentrated on another discharging passage in a moment by the enforced discharge of the fine ore due to a pressure difference, the fluidized bed is impacted. Accordingly, fine ore drops toward a lower portion of the distribution plate, and furthermore a stagnating layer is formed in and near the other discharging passage and then there is a problem in that non-fluidizing area, which is fatal to an operation of the fluidized-bed reduction reactor, is formed.
The present invention is contrived to provide a method for manufacturing molten iron that is capable of stably charging and discharging fine iron ore quickly during an emergency situation.
In addition, the present invention is contrived to provide an apparatus for manufacturing molten iron that is capable of stably charging and discharging fine iron ore quickly during an emergency situation.